May io. 1894] 



I 



NATURE 



.■?5 



occurrence. Estimates based on a thickness of from 3J to 5 

 feet, and a maximum depth of 2000 feet, give one million tons 

 as the probable quantity available. 



The Director's iri-monthly notes in the same number of the 

 Records contain a full account of the gigantic landslip in Garhwal, 

 noticed previously in Natl're (vol. xlix. p. 438). The fall 

 of rock took place last September, and dammed up the valley 

 of the Bihri Ganga by a wall 900 feet high. The water has 

 steadily accumulated behind the dam, and is now daily expected 

 to overflow. The first rush of water will be severe, and 

 probably about 250 feet of the dam will be carried away ; after 

 that there may be a permanent lake established with a natural 

 outfall. An investigation of this interesting landslip is in 

 progress by Mr. flolland. 



Dr. J. W. Gregory describes the Echinoidea of Cutch in 

 the " Pal^eontologica Indica" (ser. ix. vol. ii. part I, 1893). The 

 Echinoids are few and small ; they lived probably on sand and 

 in rock-pools in a somev^hat rough sea around a series of coral- 

 reefs. More light on the geology of the area may be expected 

 from the large collection of corals. The fauna seen-s to be 

 homotaxial with the Callovian of Europe. 



A RECENT number of the Comptts Rendus contains a note by 

 M. E. Bouiy on the capacity of a polarised surface of mercury 

 and other substances. By means of the principles of thermo- 

 dynamics, Lippmann has shown that the polarisation capacity 

 of unit surface of mercury, the surface being kept constant, is 



d"A 

 equal to - — - where A is the surface tension and ^ the counter 

 Ue- 



electromotive force of polarisation. M. Lippmann has also 

 calculated the value of this expression for mercury in contact 

 with acidulated water, and found that, at any rate within wide 

 limits, the value is independent of e. On the other hand, 

 the author, as well as Blondlot, finds that in the case of platinum 

 electrodes in different electrolytes, even when the time of charge 

 is evanescent, the capacity increases rapidly with the increase 

 uf e. The author has shown that this increase does not take 

 place if we consider that part of the capacity which is capable 

 of producing a discharge current in an external circuit, and that 

 polarisation phenomena are in part irreversible, except fcr in- 

 linitely small values of the electromotive force and the time. 

 The experiments tnus show that, if the irreversible parts of the 

 phenomena are omitted, the capacity of platinum is independent 

 "f e, just as is the case with mercury. With platinum electrodes 

 and a solution of sodium nitrate the author has found values for 

 the capacity of a square centimetre of the electrode at tem- 

 peratures between 21° and 25° of from 1772 microfarads for a 

 solution containing two equivalents of the salt per litre to 9'32 

 microfarads for a solution of o'oooi equivalents per litre. In 

 the case of distilled water (platinum electrodes) he finds the 

 capacity per square centimetre to be S'27 microfarads. 



I.N' a paper read at the Botanical Congress at Genoa, last year. 

 Prof. Saccardo calculates the number of species of plants at 

 present known as 173,706, distributed as follows : — Flowering 

 plants, 105,231 ; Kerns, 2S19 ; other Vascular Cryptogams, 565 ; 

 Mosses, 4609 ; llepaticae, 3041 ; Lichens, 5600 ; Fungi, 39,603 ; 

 AlgK, 12,178. Prof. Saccardo thinks it probable that the total 

 number of existing species of Fungi may amount to 250,000, 

 and of all other plants to 135,000. 



A sir of simple and instructive heat experiments, illustrat- 

 ing the laws of expansion, radiation, and convection, are de- 

 scribed by Dr. V. Dvor;ik in the Zeilsckii/l fur Physitalisclien 

 UnlcrriclU. To show the expansion of a solid by heat, a brass 

 wire, l*5m. long, is suspended horizontally by two clamps. A 

 weight of about 5 gr. is suspended at the middle of the wire, 



NO. 1280, VOL. 50] 



and a small wooden block is placed below it. The expansion 

 produced by passing a lighted match along the wire produces a 

 perceptible lowering of the weight. To prove that emissive 

 power is proportional to the power of absorbing radiant beat. 

 Dr. Dvor.-ik constructs a special thermo-couple, consisting of a 

 disc of thin German silver, to the back of which a thin steel 

 wire is soldered. Both are connected with a delicate galvano- 

 meter. When the disc is lamp-blacked and exposed to radiation, 

 a larger deflection is obtained than after the lamp-black has been 

 wiped oflf. A still largerdeflection is obtained when the lamp-black 

 is moistened with olive oil. .\ comparison of these indications 

 with the deflections obtained from the radiation of a Leslie cube 

 with the corresponding surfaces proves the law referred to. To 

 exhibit the phenomenon of latent heat, a plate of copper foil 

 mounted on a wooden ring is soldered to a German silver 

 wire, and both copper and wire are provided with binding 

 screws, and connected with a galvanometer. By depressing the 

 1 copper foil into the ring a shallow dish is obtained, in which 

 { liquids may be evaporated. The galvanometer shows the loss 

 j of heat attending evaporation, the amount of latent heat differ- 

 ing with the liquid used. Convection currents in air and water 

 j are, according to Dr. Dvorak, well shown by introducing the 

 liquid or gas between a screen and a point of light. The latter 

 may be produced by placing a screen with a small hole at the 

 principal focus of a lens receiving the sun's rays. A Bunsen 

 burner with a small flame, a glowing match, water containing 

 a wire heated by an electric current, or water cooled by a frag- 

 ment of ice or salt at the surface, show beautiful ascending or 

 descending clouds on the screen. 



We welcome the May number of "The Country Month by 

 Month," by Mrs. J. A. Owen and Prof. Boulger. What has 

 been said of previous issues applies to this. The book is a 

 chatty and bright companion for country rambles. 



Prof. W^ R. Fisher wishes us to state that he was not 

 present at the evening meeting of the Essex Field Club at 

 Chingford, reported in our last issue Jp. 12}. 



The quarterly Journal of the Geological Society, No. 198, 

 which has just been published, contains, in addition to the 

 papers read before the Society from November 1893 to February 

 1894, inclusive, the anniversary address of the President, " On 

 some Recent W'ork of the Geological Society," part ii. The 

 Joitrnal reaches its jubilee this year, and a suitable index to the 

 contents is being prepared to commemorate the occurrence. 



Messrs. Hachette and Co., of Paris, have begun to 

 publish, in parts, a work by M. Maspero, entitled " l.'Histoire 

 Ancienne des Peuples de I'Orient." .Maspero's book, published 

 under the same title nearly twenty years ago, has become 

 classical. That of which the publication has just been com- 

 menced, however, will only be like its predecessor in name and 

 general outline ; for the text will be new, and it is to be richly 

 illustrated. It will be divided into three volumes, issued in about 

 150 separate parts of sixteen pages each. Oriental history will 

 be scientifically treated, and the work will appeal to all 

 who are interested in the discoveries that have been made 

 in Egypt, .Vssyria, Chaldea, and Asia Minor during the last 

 thirty years. 



The March number of Modern Medicine and Baclcriological 

 I Revieii.' contains a reminiscence of Sir Andrew Clark from the 

 pen of Miss Frances E. Willard. The little article is not only 

 interesting but useful, containing an exact account of general 

 and most simple instructions recommended by Sir Andrew 

 Clark for the maintenance of health, which admit of wide 

 application. Amongst the bacteriological notes, we find a 



